On the combined use of dynamic simulations and plant data to account for fouling in heat exchanger design

Resumo

Traditional heat exchanger design methodologies prescribe the use of fixed fouling factors to account for the reduced thermal performance of heat exchangers operating in non-clean services. This practice has been criticised in the past as it does not account for the dependency of the underlying fouling mechanisms on process conditions and time, often leading to oversized equipment which exacerbate fouling. Neglecting fouling dynamics and its dependence on process conditions at the design stage has also been identified as the cause of major failures. In recognition of these limitations, much research effort has been put in recent years to improve the fundamental understanding of the various fouling mechanisms and industry has started shifting to a different paradigm which involves the use of system-specific models to account for the fouling dynamics at the design stage. This presentation proposes a novel methodology to assess the impact of fouling in heat exchanger networks and identify and evaluate heat exchanger retrofit options. The methodology is based on the combined use of historical plant data with an advanced dynamic and distributed model for shell-and-tube heat exchangers undergoing fouling. The mathematical model accounts for the growth of the fouling layer inside the exchanger's tubes as a function of process conditions and time. An industrial case study, using plant measurements from an oil refinery, will be shown to illustrate the methodology and how it can be used to identify retrofit options that provide the largest overall savings to the refinery.